I don't think there will be any problem as long as you configure memory adresses, IRQs and DMAs coorectly so you don't get any conflicts.

On my 486 I have a Sound Blaster AWE32 (a "full-size" card which means it's as long as the PC case!), and a Roland MPU-401AT with a SC daughterboard on it (forgot what it's called, but it's GS anyway). I also have a Roland MT-32 connected to the MPU-401AT.
The only problem with this setup is that all data sent through the MPU-401AT is sent both to the SC daughtercard and the MT-32. When using the SC I can of course just switch off the MT-32, but that's a little harder with the daughterboard. I solved it by connecting the outputs from both the SC and the MT-32 to a switch box which connects to the input of the SB card which in turn connects to the speakers.
(Or I used to have it like that anyway. Now I connect all ouputs - SB, MPU, MT-32 - to an external mixer meant to be used for dubbing home videos, and from that to the speakers)

One thing you should be aware of is that the MIDI interfaces on SB cards are not 100% MPU-401-compatible and might not work with all games without the use of patches. Therefore I would rather put the daughterboard on an MPU-401AT than on the SB.
On the other hand you might run out of IRQs etc with all three cards (LAPC-1, SB, MPU) installed.

All three can co-exist, provided you have the necessary IRQs and I/O ports available.

The LAPC-I card really should use I/O 330, IRQ 2/9. The IRQ is very rarely used for games anyways, so it should not conflict with something else that is using it.

The Sound Blaster 16/AWE32 should use midi I/O 300, the midi IRQ is the same as the Sound Blaster IRQ, and 5 or 7 are the most common choices.

The MPU-401AT should use any I/O port selection that is not 330 or 300. It can also use IRQ 2/9 because you won't be using the LAPC-I and the MPU-401AT at the same time.

Keep the SCB-55 on the MPU-401AT because it gives better sound quality than attached to a Sound Blaster and would be unaffected by the hanging note bug that many 16 & AWE32 cards may be plagued with.

Are you sure a LAPC-I and a MPU-401AT can share the same interrupt?
Whenever I set the same IRQ for my LAPC-I and my SCC-1, both devices won't work.

Here is my current configuration:
LAPC-I: Port 330, IRQ 2/9
SCC-1: Port 332, IRQ 3
AWE32: Port 300, IRQ 5
GUS emulation: Hijacking port 300 when needed 😈, IRQ7

5u3 wrote:

Are you sure a LAPC-I and a MPU-401AT can share the same interrupt?
Whenever I set the same IRQ for my LAPC-I and my SCC-1, both devices won't work.

I never actually tried it that way, so If they don't work for you, then please disregard what I said.

Well I didn't try a MPU-401AT either, so there is a possibility it works. But since all those "newer" Roland interfaces are supposed to be very much the same, I'm a bit skeptical.
It's a minor issue though, as you said, the IRQ is rarely used for games, so you can safely take the IRQ of an unused COM port.

5u3 wrote:

Well I didn't try a MPU-401AT either, so there is a possibility it works. But since all those "newer" Roland interfaces are supposed to be very much the same, I'm a bit skeptical.
It's a minor issue though, as you said, the IRQ is rarely used for games, so you can safely take the IRQ of an unused COM port.

I sincerely doubt it, all the Roland cards use essentially the same hardware, unchanged since 1985.

It maybe an old thread, but i want to know which switch box you are using to connect multiple outputs to one speaker set..

puttesnutte wrote on 2007-10-28, 18:49:

On my 486 I have a Sound Blaster AWE32 (a "full-size" card which means it's as long as the PC case!), and a Roland MPU-401AT with a SC daughterboard on it (forgot what it's called, but it's GS anyway). I also have a Roland MT-32 connected to the MPU-401AT.

That's not a full size card.. THIS is a full size card:

Pardon for the Paul Hogan pastiche and thread necromancy, but the Roland LAPC-I from around 1989 is enormous, 330 mm (13") length and about 122 mm tall (4"), and I am struggling to find a home for it in a P2 / P3 era PC to house it. Have spotted an IBM 300PL 6862, but not sure if it can actually fit the Roland LAP-I. Wish I was able to get confirmation, but it is proving to be quite hard.

An AWE 64 for comparison:

This one is 330mm long.